Note: Descriptions are shown in the official language in which they were submitted.
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Method for dehydrating a carbohydrate-comprising composition
Description
The present invention relates to a method for dehydrating a carbohydrate-
comprising
composition.
In the economic exploitation of valuable materials from biomass feedstocks,
especially
the dehydration products from diverse carbohydrate sources are ascribed great
potential. Hexoses are the most widespread monosaccharides in nature, and
especially
D-fructose and D-glucose are available in adequate quantities and economically
good
conditions. The conversion of hexoses to furan products is a particularly
highly
promising approach. In this case, especially 5-hydroxymethylfurfural (5-HMF),
i.e. the
dehydration product of hexoses, has a key role. It can serve, inter alia, as
starting point
for the synthesis of pharmaceuticals, polymers and macrocyclic compounds.
Derivatives thereof include, e.g., 2,5-furfuryldiamine, 2,5-furfuryl
diisocyanate and 5-
hydroxymethylfurfurylidene ester, which can serve for producing polyesters,
polyamides and polyurethanes.
Avelino Corma, Sara lborra, and Alexandra Velty, in Chem. Rev. 2007, 107, 2411-
2502, describe diverse chemical routes for converting biomass into chemicals,
inter alia
under point 2.2.1, the dehydration of monosaccharides, and especially acid-
catalyzed
dehydration of fructose. Methods in the presence of water have the
disadvantage of
partial rehydration of the resultant 5-HMF. This disadvantage can be avoided
by, e.g.,
simultaneous extraction of the resultant 5-HMF using an organic solvent, or
carrying
out the dehydration in an organic solvent. Good yields are achieved, e.g.,
when the
reaction is carried out in DMSO. It is disadvantageous of this variant,
however, that
DMSO may only be separated off with difficulty from 5-HMF and that toxic
sulfur-
comprising by-products are formed. Carrying out the reaction in 1-butyl-3-
methylimidazolium tetrafluoroborate, i.e. in an ionic solvent, is also
mentioned. After a
reaction time of three hours at 80 C, 5-HMF could be achieved in 50% yield. By
using
DMSO as a cosolvent and extending the reaction time to 24 hours, a yield
increase to
80% could be achieved.
Xinli Tong, Yang Ma and Yongdan Li, in Applied Catalysis A: General 385 (2010)
1-13,
describe the use of sugars for producing furan chemicals, and especially the
synthesis
of 5-hydroxymethylfurfural (5-HMF), 2,5-furandicarboxylic acid (2,5-FDCA), 2,5-
diformylfuran (2,5-DFF), 2,5-bis(hydroxymethyl)furan (2,5-BHF) and 2,5-
dimethylfuran
(2,5-DMF) from various carbohydrate sources such as fructose, glucose,
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polysaccharides and biomass feedstocks. Methods based on various catalysts,
such as
mineral acids, organic acids, solid acids and metal-comprising catalysts, are
described.
Yu Su, Heather M. Brown, Xiwen Huang, Xiao-dong Zhou, James E. Amonette and
Z. Conrad Zhang, in Applied Catalysis A: General, Volume 361, Issues 1-2,20
June
2009, pages 117-122, describe the single-stage conversion of cellulose to 5-
HMF. A
pair of metal chlorides (CuCl2 and CrCl2) dissolved in 1-ethyl-3-
methylimidazolium
chloride ([EMIIACI) catalyzes, at temperatures of 80 to 120 C, the reaction
with high
purity. In this case cellulose depolymerization is a power of ten more rapid
than the
acid-catalyzed reaction.
Ken-ichi Shimizu, Rie Uozumi and Atsushi Satsuma, in Catalysis Communications
10
(2009), pages 1849-1853, describe an improved method for producing 5-HMF from
fructose in the presence of solid acid catalysts, such as heteropolyacids,
zeolites and
acid ion-exchange resins, by continuous removal of water from the reaction
mixture by
a slight reduced pressure.
There continues to be a requirement for economic methods for producing
dehydration
products from diverse carbohydrate sources. These are intended to make
possible
rapid, continuous and/or selective production. They are intended, in
particular, to be
suitable for producing 5-hydroxymethylfurfural (5-HMF) from hexoses and
carbohydrate
sources comprising hexoses.
Surprisingly, it has been found that this object is achieved by a method in
which a
carbohydrate-comprising composition that comprises at least one low-boiling
solvent
and at least one ionic liquid is subjected to a dehydration and simultaneous
evaporation of the low-boiling solvent and at least some of the dehydration
products
formed, and a gaseous discharge from the dehydration/evaporation zone is taken
off
continuously.
The invention therefore relates to a continuous method for dehydrating a
carbohydrate-
comprising composition, which comprises
i) providing a composition which comprises
35- at least one carbohydrate,
- at least one ionic liquid (IL), and
- at least one solvent (LM) that has a boiling point of a maximum
of 120 C
under standard pressure (1013 mbar),
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ii) feeding the composition of step i) into an evaporator and subjecting
it to a
reaction and evaporation at a temperature in a range from 100 to 300 C and a
pressure of a maximum of 500 mbar,
iii) taking off from the evaporator a gaseous discharge which comprises the
dehydration product, and taking off a liquid discharge which comprises at
least
one ionic liquid,
iv) condensing the gaseous discharge and subjecting it to a separation
with isolation
of the dehydration product.
The method according to the invention in embodiments thereof described
hereinafter is
advantageous with respect to one or more of the following points:
- short residence times in the evaporator;
- continuous method;
- no catalyst required;
- advantageous combination of dehydration in the presence of an ionic
solvent and
separation by distillation of the resultant dehydration products in a water-
comprising, gaseous stream;
- good separation of the resultant dehydration products from the ionic
liquid (IL) by
gaseous discharge together with the solvent (LM);
- the ionic liquid (IL) present in the liquid discharge is substantially
free from the
solvent (LM) which is vaporized and discharged in the gaseous state;
- the ionic liquid (IL) present in the liquid discharge is substantially
free from the
water formed in the dehydration reaction, which water is vaporized and
discharged in the gaseous state;
- a deactivation of the ionic liquid (IL) due to accumulation of water is
avoided.
Even when the gaseous discharge taken off from the evaporator according to the
method according to the invention generally comprises the dehydration products
only in
the one figure percentage range, the method according to the invention is
nevertheless
advantageous compared with the known batch methods. Thus the residence time in
the evaporator is only in the range of seconds to a few minutes compared with
many
hours in the known methods. The space-time yield of the method according to
the
invention is correspondingly high. The short residence time, the rapid removal
of the
resultant dehydration products in the gas stream and the immediately
subsequent
condensation enable control of the method with respect to the dehydration
product
sought as target component. In contrast, the known batch methods lead to
constant
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rehydration and an equilibration of various enolates and therefore to the
formation of a
complex product spectrum.
The method according to the invention makes possible the production of
dehydration
products from carbohydrate-comprising starting materials, wherein the use of
the
customary catalysts known from the prior art for such dehydration reactions
can be
dispensed with. The carbohydrate-comprising composition used according to the
invention for the dehydration is not obligatorily additionally brought into
contact with
mineral acids, organic acids, acid solid catalysts, such as heteropolyacids,
zeolites,
and acid ion-exchange resins and metal-comprising catalysts.
The expression "solubilization", in the context of the invention, denotes the
conversion
into a liquid state and comprises here the generation of solutions of the
carbohydrate-
comprising starting material and also the conversion into a solubilized state
different
therefrom. If a polysaccharide, a cellulose material or a lignocellulose
material is
converted into a solubilized state, the individual polymer molecules need not
be
necessarily completely surrounded by a solvate sheath. It is critical that the
polymer
converts into a liquid state owing to the solubilization. Solubilized
substances in the
context of the invention are therefore also colloidal solutions,
microdispersions, gels,
etc.
Providing a carbohydrate-comprising composition (step i)
Preferably, the composition provided in step i) has a content of the
carbohydrate-
comprising starting material in the range from 1 to 20% by weight,
particularly
preferably in the range from 2 to 15% by weight, based on the total weight of
the
composition.
In the context of the present invention, the expression "carbohydrate-
comprising
composition" comprises compositions which comprise monosaccharides,
oligosaccharides, polysaccharides and mixtures thereof. The expression
"oligosaccharides" denotes carbohydrates which have two to six monosaccharide
units.
The expression "polysaccharides" denotes carbohydrates which have more than
six
monosaccharide units. Typical members of the polysaccharides are, e.g.,
celluloses,
starches and glycogens.
In a first preferred embodiment, the carbohydrate-comprising starting material
is
selected from mono- and/or oligosaccharides. Especially, the carbohydrate-
comprising
starting material is selected from mono- and/or disaccharides.
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Preferably, the mono- and/or oligosaccharides are selected from
- aldopentoses,
5 - aldohexoses,
- ketohexoses,
- disaccharides that are derived from aldopentoses, aldohexoses,
ketohexoses
and mixtures thereof, and
- mixtures thereof.
Particularly preferably, the mono- and/or oligosaccharides are selected from
fructose,
glucose, sucrose, xylose and mixtures thereof.
A preferred embodiment of the method according to the invention is dehydrating
fructose for producing 5-hydroxymethylfurfural (5-HMF).
A preferred embodiment of the method according to the invention is dehydrating
sucrose for producing 5-hydroxymethylfurfural (5-HMF).
A preferred embodiment of the method according to the invention is dehydrating
xylose
for producing furfural.
In a second preferred embodiment, the carbohydrate-comprising starting
material is
selected from cellulosic starting materials.
Suitable as carbohydrate-comprising starting material for the method according
to the
invention are, in addition, enzymatic breakdown products of cellulosic or
lignocellulosic
starting materials.
Ionic liquid (IL)
Ionic liquids, in the context of the present application, denote organic salts
which are
already liquid at temperatures below 180 C. Preferably, the ionic liquids have
a melting
point of below 150 C, particularly preferably below 120 C, in particular below
100 C.
Ionic liquids which are already in the liquid state at room temperature are
described, for
example, by K. N. Marsh et al., Fluid Phase Equilibria 219 (2004), 93 - 98 and
J. G. Huddleston et al., Green Chemistry 2001, 3, 156- 164.
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Ionic liquids suitable for use in the method according to the invention are
described in
WO 2008/090155 and WO 2008/090156, which are hereby incorporated herein by
reference.
Cations and anions are present in the ionic liquid. In this case, within the
ionic liquid, a
proton or an alkyl radical can be transferred from the cation to the anion,
whereby two
neutral molecules result. In the ionic liquid used according to the invention,
therefore,
an equilibrium of anions, cations and neutral molecules formed therefrom can
be
present.
Preferred ionic liquids are combinations of nitrogenous cation components
(such as
imidazolium derivatives) and halogen ions as anions.
Suitable compounds which are suitable for forming the cation of ionic liquids
are
described, e.g., in DE 102 02 838 A1. These compounds preferably comprise at
least
one heteroatom such as, e.g., 1 to 10 heteroatoms, which are preferably
selected from
nitrogen, oxygen, phosphorus and sulfur atoms. Preference is given to
compounds
which comprise at least one nitrogen atom and optionally additionally at least
one
further heteroatom different from nitrogen. Preference is given to compounds
which
comprise at least one nitrogen atom, particularly preferably 1 to 10 nitrogen
atoms, in
particular 1 to 5 nitrogen atoms, very particularly preferably 1 to 3 nitrogen
atoms, and
especially 1 or 2 nitrogen atoms. The last-mentioned nitrogen compounds can
comprise further heteroatoms such as oxygen, sulfur or phosphorus atoms.
The nitrogen atom is, e.g., a suitable carrier of the positive charge in the
cation of the
ionic liquid. For the case that the nitrogen atom is the carrier of the
positive charge in
the cation of the ionic liquid, in the synthesis of the ionic liquids, first,
by quaternization
at the nitrogen atom, for instance of an amine or nitrogen heterocycle, a
cation can be
generated. The quaternization can be performed by protonation of the nitrogen
atom.
Depending on the protonation reagent used, salts having differing anions are
obtained.
In cases in which it is not possible to form the desired anion as soon as
during the
quaternization, this can proceed in a further synthesis step. Proceeding, for
example,
from an ammonium halide, the halide can be reacted with a Lewis acid, wherein
a
complex anion is formed from halide and Lewis acid. Alternatively thereto,
exchange of
a halide ion for the desired anion is possible. This can be achieved by adding
a metal
salt, with precipitation of the metal halide formed, via an ion exchanger, or
by
displacement of the halide ion by a strong acid (with release of the
hydrohalic acid).
Suitable methods are described, for example, in Angew. Chem. 2000, 112, pp.
3926 -
3945 and the literature cited therein.
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Preference is given to those compounds that comprise at least one five- to six-
member
heterocycle, in particular a five-member heterocycle which has at least one
nitrogen
atom and also possibly one oxygen atom or sulfur atom. Particular preference
is given
to those compounds that comprise at least one five- to six-member heterocycle
which
has one, two or three nitrogen atoms, and one sulfur atom or one oxygen atom,
very
particular preference to those having two nitrogen atoms. Further preference
is given to
aromatic heterocycles.
Particularly preferred compounds are those that have a molar mass of less than
1000 g/mol, very particularly preferably less than 800 g/mol, and in
particular less than
500 g/mol.
Preferred cations are pyridinium ions. These are selected, in particular, from
pyridinium, 2-methylpyridinium, 2-ethylpyridinium, 5-ethyl-2-methylpyridinium
and 2-
methyl-3-ethylpyridinium and also 1-methylpyridinium, 1-ethylpyridinium, 1-(1-
butyl)-
pyridinium, 1-(1-hexyl)pyridinium, 1-(1-octyl)pyridinium, 1-(1-
hexyl)pyridinium, 1-(1-
octyl)pyridinium, 1-(1-dodecyl)pyridinium, 1-(1-tetradecyl)pyridinium, 1-(1-
hexadecyI)-
pyridinium, 1,2-dimethylpyridinium, 1-ethyl-2-methylpyridinium, 1-(1-butyl)-2-
methyl-
pyridinium, 1-(1-hexyl)-2-methylpyridinium, 1-(1-octyI)-2-methylpyridinium, 1-
(1-
dodecyI)-2-methylpyridinium, 1-(1-tetradecyI)-2-methylpyridinium, 1-(1-
hexadecyI)-2-
methylpyridinium, 1-methyl-2-ethylpyridinium, 1,2-diethylpyridinium, 1-(1-
butyl)-2-ethyl-
pyridinium, 1-(1-hexyl)-2-ethylpyridinium, 1-(1-octyI)-2-ethylpyridinium, 1-(1-
dodecyI)-2-
ethylpyridinium, 9-(1-tetradecyI)-2-ethylpyridinium, 1-(1-hexadecyI)-2-
ethylpyridinium,
1,2-dimethy1-5-ethylpyridinium, 1,5-diethy1-2-methylpyridinium, 1-(1-butyl)-2-
methyl-3-
ethylpyridinium, 1-(1-hexyl)-2-methyl-3-ethylpyridinium and 1-(1-octyI)-2-
methyl-3-
ethylpyridinium, 1-(1-dodecyI)-2-methyl-3-ethylpyridinium, 1-(1-tetradecyI)-2-
methyl-3-
ethylpyridinium and 1-(1-hexadecyI)-2-methyl-3-ethylpyridinium.
Preferred cations are, in addition, unsubstituted or substituted pyridazinium
ions.
Preferred cations are, in addition, unsubstituted or substituted pyrimidinium
ions.
Preferred cations are, in addition, unsubstituted or substituted pyrazinium
ions.
Preferred cations are, in addition, unsubstituted or substituted imidazolium
ions.
Particularly suitable imidazolium ions are 1-methylimidazolium, 1-
ethylimidazolium, 1-
(1-propyl)imidazolium, 1-(1-allyl)imidazolium, 1-(1-butyl)imidazolium, 1-(1-
octyI)-
imidazolium, 1-(1-dodecyl)imidazolium, 1-(1-tetradecyl)imidazolium, 1-(1-
hexadecyI)-
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imidazolium, 1,3-dimethylimidazolium, 1,3-diethylimidazolium, 1-ethyl-3-methyl-
imidazolium, 1-(1-butyl)-3-methylimidazolium, 1-(1-butyl)-3-ethylimidazolium,
1-(1-
hexyl)-3-methylimidazolium, 1-(1-hexyl)-3-ethylimidazolium, 1-(1-hexyl)-3-
butyl-
imidazolium, 1-(1-octyI)-3-methylimidazolium, 1-(1-octyI)-3-ethylimidazolium,
1-(1-
octyI)-3-butylimidazolium, 1-(1-dodecyI)-3-methylimidazolium, 1-(1-dodecyI)-3-
ethyl-
imidazolium, 1-(1-dodecyI)-3-butylimidazolium, 1-(1-dodecyI)-3-
octylimidazolium, 1-(1-
tetradecyI)-3-methylimidazolium, 1-(1-tetradecyI)-3-ethylimidazolium, 1-(1-
tetradecyI)-3-
butylimidazolium, 1-(1-tetradecyI)-3-octylimidazolium, 1-(1-hexadecyI)-3-
methyl-
imidazolium, 1-(1-hexadecyI)-3-ethylimidazolium, 1-(1-hexadecyI)-3-
butylimidazolium,
1-(1-hexadecyI)-3-octylimidazolium, 1,2-dimethylimidazolium, 1,2,3-trimethyl-
imidazolium, 1-ethyl-2,3-dimethylimidazolium, 1-(1-butyl)-2,3-
dimethylimidazolium, 1-
(1-hexyl)-2,3-dimethylimidazolium, 1-(1-octyI)-2,3-dimethylimidazolium, 1,4-
dimethyl-
imidazolium, 1,3,4-trimethylimidazolium, 1,4-dimethy1-3-ethylimidazolium, 3-
methyl-
imidazolium, 3-ethylimidazolium, 3-n-propylimidazolium, 3-n-butylimidazolium,
1,4-
dimethy1-3-octylimidazolium, 1,4,5-trimethylimidazolium, 1,3,4,5-tetramethyl-
imidazolium, 1,4,5-trimethy1-3-ethylimidazolium, 1,4,5-trimethy1-3-
butylimidazolium,
1,4,5-trimethy1-3-octylimidazolium, 1-prop-1-en-3-y1-3-methylimidazolium and 1-
prop-1-
en-3-y1-3-butylimidazolium. Especially suitable imidazolium ions (IVe) are 1,3-
diethyl-
imidazolium, 1-ethyl-3-methylimidazolium, 1-(n-butyl)-3-methylimidazolium.
Preferred cations are, in addition, unsubstituted or substituted pyrazolium
ions.
Particularly preferred pyrazolium ions are pyrazolium and 1,4-
dimethylpyrazolium.
Preferred cations are, in addition, unsubstituted or substituted pyrazolinium
ions.
Preferred cations are, in addition, unsubstituted or substituted imidazolinium
ions.
Preferred cations are, in addition, unsubstituted or substituted thiazolium
ions.
Preferred cations are, in addition, unsubstituted or substituted 1,2,4-
triazolium ions.
Preferred cations are, in addition, unsubstituted or substituted pyrrolidinium
ions.
Preferred cations are, in addition, unsubstituted or substituted
imidazolidinium ions.
Preferred cations are, in addition, unsubstituted or substituted ammonium
ions.
Examples of the tertiary amines from which the quaternary ammonium ions are
derived
by quaternization with said radical R are diethyl-n-butylamine, diethyl-tert-
butylamine,
diethyl-n-pentylamine, diethylhexylamine, diethyloctylamine, diethyl(2-
ethylhexyl)-
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amine, di-n-propylbutylamine, di-n-propyl-n-pentylamine, di-n-
propylhexylamine, di-n-
propyloctylamine, di-n-propy1(2-ethylhexyl)amine, diisopropylethylamine,
diisopropyl-n-
propylamine, diisopropylbutylamine, diisopropylpentylamine,
diisopropylhexylamine,
diisopropyloctylamine, diisopropy1(2-ethylhexyl)amine, di-n-butylethylamine,
di-n-butyl-
n-propylamine, di-n-butyl-n-pentylamine, di-n-butylhexylamine, di-n-
butyloctylamine, di-
n-butyl-(2-ethylhexyl)amine, N-n-butylpyrrolidine, N-sec-butylpyrrolidine, N-
tert-butyl-
pyrrolidine, N-n-pentylpyrrolidine, N,N-dimethylcyclohexylamine, N,N-
diethylcyclohexyl-
amine, N,N-di-n-butylcyclohexylamine, N-n-propylpiperidine, N-
isopropylpiperidine, N-
n-butylpiperidine, N-sec-butylpiperidine, N-tert-butylpiperidine, N-n-
pentylpiperidine,
N-n-butylmorpholine, N-sec-butylmorpholine, N-tert-butylmorpholine, N-n-pentyl-
morpholine, N-benzyl-N-ethylaniline, N-benzyl-N-n-propylaniline, N-benzyl-N-
isopropyl-
aniline, N-benzyl-N-n-butylaniline, N,N-dimethyl-p-toluidine, N,N-diethyl-p-
toluidine,
N,N-di-n-butyl-p-toluidine, diethylbenzylamine, di-n-propylbenzylamine, di-n-
butyl-
benzylamine, diethylphenylamine, di-n-propylphenylamine and di-n-
butylphenylamine.
Preferred tertiary amines are diisopropylethylamine, diethyl-tert-butylamine,
diiso-
propylbutylamine, di-n-butyl-n-pentylamine, N,N-di-n-butylcyclohexylamine and
also
tertiary amines of pentyl isomers. Particularly preferred tertiary amines are
di-n-butyl-n-
pentylamine, and tertiary amines from pentyl isomers. A further preferred
tertiary amine
which has three identical radicals is triallylamine.
Preferred cations are, in addition, unsubstituted or substituted guanidinium
ions. A very
particularly preferred guanidinium ion is N,N,N',N',N",N"-
hexamethylguanidinium.
Preferred cations are, in addition, unsubstituted or substituted cholinium
ions.
Preferred cations are, in addition, unsubstituted or substituted cations of
1,5-diaza-
bicyclo[4.3.0]non-5-ene (DBN) and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU).
Preferred cations are, in addition, unsubstituted or substituted phosphonium
ions.
Preferred cations are, in addition, unsubstituted or substituted sulfonium
ions.
Of the abovementioned heterocyclic cations, the imidazolium ions,
imidazolinium ions,
pyridinium ions, pyrazolinium ions and pyrazolium ions are preferred.
Particular
The anion of the ionic liquid is for example selected from
1.) Anions of the formulae: F-, CI-, Br -, I-, BF4-, PFs-, CF3S03-,
(CF3S03)2N-, CF3CO2-,
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CCI3002-, CN-, SCN-, OCN-.
2.) Anions of the formulae: S042-, HSO4-, S032-, HS03-, Rc0503-, Rc503-.
5 3.) Anions of the formulae: P043-, HP042-, H2PO4-, RcP042-, HIRcPO4-,
RcRdPO4-.
4.) Anions of the formulae: RcHP03-,RcRdP02-, RcRdP03-.
5.) Anions of the formulae: P033-, HP032-, H2P03-, RcP032-, RcHP03-,
RcRdP03-.
6.) Anions of the formulae: RcRdP02-, RcHP02-, RcRdP0-, RcHP0-.
7.) Anions of the formula RcC00-.
8.) Anions of the formulae: B033-, HB032-, H2B03-, RcRdB03-, RcHB03-, RcB032-,
B(ORc)(0Rd)(0Re)(ORT, B(H504)4-, B(Rc504)4-.
9.) Anions of the formulae: RcB022-, RcRdB0-.
10.) Anions of the formulae: HCO3-, C032-, RcCO3-.
11.) Anions of the formulae: Si044 , H5i043 , H25i042 , H35iO4 , Rc5i043 ,
RcRdSi042-,
RcRdReSiO4-, HIRcSi042-, H2RcSiO4-, HIRcRdSiO4-.
12.) Anions of the formulae: Rc5i033-, RcRdSi022-, RcRdReSi0-, RcRdReSiO3-,
RcRdReSi02-, RcRdSi032-.
13.) Anions of the formulae:
NC,
,N
N
C
O 0 O 00
\\ Rc Z( Rc¨S
_ Rc¨S
Rd
R¨S1
Rd
0 0 0
0
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14.) Anions of the formulae:
SO -It
1 2
C
\S02-Rd
Re-02S
15.) Anions of the formula RcO-.
16.) Anions of the formulae HS-, [S]2-, [HS], [RCS]-, wherein v is a positive
integer
from 2 to 10.
The radicals Rc, Rd, Re and Rf are, preferably independently of one another,
- hydrogen;
- unsubstituted or substituted alkyl, preferably unsubstituted or
substituted 01-030
alkyl, particularly preferably unsubstituted or substituted 01-018 alkyl which
can
be interrupted by at least one heteroatom or heteroatom-comprising group;
- unsubstituted or substituted aryl, preferably unsubstituted or
substituted 06-014
aryl, particularly preferably unsubstituted or substituted 06-010 aryl;
- unsubstituted or substituted cycloalkyl, preferably unsubstituted or
substituted
05-012 cycloalkyl;
- unsubstituted or substituted heterocycloalkyl, preferably unsubstituted
or
substituted heterocycloalkyl having 5 or 6 ring atoms, wherein the ring, in
addition
to carbon ring atoms, comprises 1, 2 or 3 heteroatoms or heteroatom-comprising
groups;
- unsubstituted or substituted heteroaryl, preferably unsubstituted or
substituted
heteroaryl having 5 to 10 ring atoms, wherein the ring, in addition to carbon
ring
atoms, comprises 1, 2 or 3 heteroatoms or heteroatom-comprising groups, which
are selected from oxygen, nitrogen, sulfur and NRa;
wherein, in anions that comprise a plurality of radicals Rc to Rf, also in
each case
two of these radicals, together with the part of the anion to which they are
bound,
can be at least one saturated, unsaturated or aromatic ring or a ring system
having 1 to 12 carbon atoms, wherein the ring or the ring system can comprise
1
to 5 non-adjacent heteroatoms or heteroatom-comprising groups, that are
preferably selected from oxygen, nitrogen, sulfur and NRa, and wherein the
ring
or the ring system is unsubstituted or can be substituted.
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Preferred anions are CI-, Br, formate, acetate, propionate, butyrate, lactate,
saccharinate, carbonate, hydrogencarbonate, sulfate, sulfite, 01-04
alkylsulfates,
methanesulfonate, tosylate, trifluoroacetate, 01-04 dialkylphosphates and
hydrogensulfate.
Particularly preferred anions are CI-, Br, H000-, CH3C00-, CH3CH2C00-,
carbonate,
hydrogencarbonate, sulfate, sulfite, tosylate, CH3S03- or CH30S03-.
In particular, the anions are selected from Cl- and Br .
Suitable ionic liquids for use in the method according to the invention are
commercially
available, e.g. under the brand name Basionic from BASF SE.
Advantageous compounds for use in the method according to the invention are,
e.g.:
1-ethyl-3-methylimidazolium chloride (EMIM Cl, Basionic ST 80)
1-ethyl-3-methylimidazolium methanesulfonate (EMIM CH3503, Basionic ST 35),
1-butyl-3-methylimidazolium chloride (BMIM Cl, Basionic ST 70),
1-butyl-3-methylimidazolium methanesulfonate (BMIM CH3503, Basionic ST 78),
methylimidazolium chloride (HMIM Cl, Basionic AC 75),
methylimidazolium hydrogensulfate (HMIM H504 Basionic AC 39),
1-ethyl-3-methylimidazolium hydrogensulfate (EMIM H504 Basionic AC 25),
1-butyl-3-methylimidazolium hydrogensulfate (BMIM H504 Basionic AC 28)
1-ethyl-3-methylimidazolium acetate (EMIM Acetate, Basionic BC 01),
1-butyl-3-methylimidazolium acetate (BMIM Acetate, Basionic BC 02).
Particular preference is given to 1-ethyl-3-methylimidazolium chloride, 1-
butyl-3-methyl-
imidazolium chloride, methylimidazolium chloride, 1-ethyl-3-methylimidazolium
acetate,
1-butyl-3-methylimidazolium acetate and mixtures thereof. Those which are
especially
suitable are 1-butyl-3-methylimidazolium chloride and methylimidazolium
chloride.
Solvents (LM)
The composition provided in step i) comprises at least one solvent (LM) that
has a
boiling point of a maximum of 120 C under standard conditions (100 C, 1013
mbar).
The solvent (LM) used in step i) is preferably selected from water and
mixtures of water
and at least one water-miscible organic solvent.
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Preferred water-miscible organic solvents are selected from methanol, ethanol,
n-propanol, isopropanol, n-butanol, dioxane, tetrahydrofuran and mixtures
thereof.
Preferably, the solvent (LM) used is a water-alcohol mixture, in particular a
water-
methanol mixture.
Preferably, in step i), as solvent (LM), a mixture of water and at least one
water-
miscible organic solvent in a weight ratio of 10:90 to 90:10, particularly
preferably 25:75
to 75:25, in particular 40:60 to 60:40, is used.
Particularly preferably, in step i), the solvent (LM) used is a mixture of
water and at
least one alcohol in a weight ratio of 10:90 to 90:10, particularly preferably
25:75 to
75:25, in particular 40:60 to 60:40.
In particular, in step i), the solvent (LM) used is a mixture of water and
methanol in a
weight ratio of 10:90 to 90:10, particularly preferably 25:75 to 75:25, in
particular 40:60
to 60:40.
Preferably, in the carbohydrate-comprising composition provided in step i),
the weight
ratio of ionic liquid (IL) to solvent (LM) is in a range from 99.5:0.5 to
50:50, particularly
preferably 99:1 to 75:25.
For providing the carbohydrate-comprising composition in step i), the
carbohydrate-
comprising starting material can be brought into intimate contact with the
ionic liquid
(IL) and/or the solvent (LM). In this process the carbohydrate-comprising
starting
material is at least partially, preferably completely, solubilized. If
necessary, the
carbohydrate-comprising starting material is subjected in advance to a
pretreatment
step for removing insoluble components, and/or insoluble components are
separated
off from the carbohydrate-comprising composition before it is fed into the
evaporator.
For providing the carbohydrate-comprising composition in step i), the
carbohydrate-
comprising starting material and the ionic liquid (IL) and/or the solvent (LM)
can be
mechanically mixed and stirred up to complete dissolution.
Preferably, for providing the carbohydrate-comprising composition in step i),
the at
least one ionic liquid (IL) and the at least one solvent (LM) are brought into
contact with
one another immediately before entry into the evaporator. Immediately before
entry into
the evaporator means that the time period from the start of the contacting
until entry
into the evaporator is at most five minutes, particularly preferably at most
one minute.
The carbohydrate-comprising starting material can, before the start of the
contacting,
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be present solely in the solvent (LM) or solely in the ionic liquid, or partly
in the solvent
(LM) and partly in the ionic liquid.
Preferably, the ionic liquid (IL), for providing the carbohydrate-comprising
composition
in step i), is warmed to a temperature above the temperature of the
surroundings
(23 C). Preferably, the ionic liquid (IL) used for providing the carbohydrate-
comprising
composition in step i) has a temperature of at least 50 C, preferably at least
75 C.
In a special embodiment, the method according to the invention serves for
dehydrating
a mono- and/or oligosaccharide-comprising composition, wherein, in step i):
i1) at least one monosaccharide and/or at least one oligosaccharide is
dissolved in a
water-alcohol mixture,
i2) the solution obtained in step i1) is mixed with at least one ionic
liquid (IL),
i3) the mixture obtained in step i2) is fed immediately subsequently into
the
evaporator of step ii).
To feed immediately subsequently into the evaporator means that the time
period from
the start of the mixing time in step i2) until entry of the mixture into the
evaporator is at
most five minutes, particularly preferably at most one minute.
Step ii)
In step ii) of the method according to the invention, the composition of step
i) is fed into
an evaporator and, at elevated temperature and reduced pressure, the
carbohydrates
present are subjected to a dehydration and simultaneously at least some of the
dehydration products formed and the solvent (LM) are vaporized.
As evaporator in step i), preferably an evaporator having a short residence
time is
used. Advantageously, a low thermal stress of the dehydration products formed
is
achieved thereby.
Suitable evaporators are, in principle, a device customary therefor, which in
the
simplest case comprises a container having heatable heat-exchange surfaces.
Preferably, a thin-film evaporator or a short-path evaporator is used. Short-
path
evaporators operate according to the same principle as thin-film evaporators,
but have
a built-in condenser. The path of the vapors to the condenser is extremely
short in the
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short-path evaporator thereby. A suitable thin-film evaporator is the falling-
film
evaporator, e.g. a vertical-tube evaporator which can additionally be provided
with tube
bundles. Preference is given to evaporators having moveable internals in
which, e.g.,
wiper blades generate a thin liquid film on the internal wall of the
evaporator (wiped-film
5 evaporator, wiper-blade evaporator). These include thin-film evaporators
of the
"LUWA" or "SAMBAY" types.
The evaporator used according to the invention in step ii) is preferably
arranged
substantially vertically. The evaporator inlet for feed of the composition
from step i) is
10 preferably located in the upper region of the evaporator. Preferably,
the evaporator inlet
is situated in the upper third, in particular in the upper quarter of the
evaporator. The
evaporator outlet for removal of the liquid discharge is situated in the lower
region of
the evaporator. Preferably, the evaporator outlet is situated in the lower
third, in
particular in the lower quarter of the evaporator. Especially, the evaporator
outlet is
15 situated at the bottom end of the evaporator. The composition of step i)
is fed into the
evaporator in the upper region and forms, on flowing down on the side walls, a
film
which is heated by a suitable heater. In this process the at least one solvent
(LM),
which under standard conditions (100 C, 1013 mbar) has a boiling point of a
maximum
of 120 C, at least partially vaporizes. At the same time, under the reaction
conditions in
the evaporator, dehydration of the carbohydrate-comprising starting material
takes
place. From the evaporator, a gaseous discharge is taken off which comprises
the
dehydration product and at least some of the at least one solvent (LM). The
gaseous
discharge is preferably discharged in the upper region of the evaporator used
according to the invention. In particular, the gaseous discharge is discharged
at the top
end of the evaporator used according to the invention.
The evaporator can be supplied with heat in a suitable manner, for example
with
steam.
The temperature in the evaporator is preferably in a range from 100 to 300 C,
particularly preferably in a range from 150 C to 250 C.
The pressure in the evaporator is preferably a maximum of 500 mbar. The
pressure in
the evaporator is particularly preferably in a range from 250 mbar to 0.1
mbar, in
particular 100 mbar to 1 mbar.
The residence time in the evaporator, based on the ionic liquid (IL) is
preferably in a
range from 0.1 second to 2 minutes, particularly preferably 1 second to 1
minute.
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Step iii)
From the evaporator, a gaseous discharge is taken off which comprises the
dehydration product, and a liquid discharge is taken off which comprises the
at least
one ionic liquid (IL).
Preferably, the gaseous discharge taken off from the evaporator in step iii)
comprises
at least 75% by weight, particularly preferably at least 90% by weight, in
particular at
least 95% by weight, of the solvent (LM), based on the total amount of the
solvent (LM)
provided in step i).
Preferably, the gaseous discharge taken off from the evaporator in step iii)
comprises
at least 75% by weight, particularly preferably at least 90% by weight, in
particular at
least 95% by weight, of the solvent (LM), based on the total amount of the
solvent (LM)
provided in step i).
Preferably, the gaseous discharge taken off from the evaporator in step iii)
comprises
at least 0.1% by weight, particularly preferably at least 0.5% by weight, in
particular at
least 1% by weight, of dehydration products, based on the total weight of the
condensed gaseous discharge.
Preferably, the liquid discharge taken off from the evaporator in step iii)
comprises at
least 90% by weight, particularly preferably at least 95% by weight,
especially at least
99% by weight, of the ionic liquid (IL), based on the total amount of the
ionic liquid
provided in step i).
Preferably, the liquid discharge taken off from the evaporator in step iii)
has a water
content of a maximum of 5% by weight, particularly preferably a maximum of 1%
by
weight, in particular a maximum of 0.5% by weight, based on the total weight
of the
liquid discharge.
The liquid discharge from the reaction zone comprises the proportions of
reaction
products of the carbohydrate-comprising starting material which are not
discharged
from the evaporator together with the gaseous discharge. The liquid discharge
from the
reaction zone comprises, in addition, the unreacted proportions of the
carbohydrate-
comprising starting material that are not discharged from the evaporator
together with
the gaseous discharge.
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Preferably, the ionic liquid (IL) present in the liquid discharge is used
again in step i) of
the method according to the invention. In this case the reaction products that
are
present of the carbohydrate-comprising starting material and the unreacted
proportions
of the carbohydrate-comprising starting material are generally uncritical.
If desirable, the liquid discharge can be subjected to at least one
purification step in
order to remove at least in part the residual components present in the ionic
liquid (IL).
This includes, e.g., extraction with a suitable extraction medium, such as
water.
In a further embodiment, the liquid discharge is subjected to a precipitation
of at least
some of the components present in the ionic liquid by a suitable precipitant.
A
precipitation is suitable, especially, for removing relatively high-molecular-
weight
components, e.g. polysaccharides and the relatively high-molecular-weight
breakdown
products thereof such as cellulose, hemicellulose, etc. Suitable precipitants
are known
to those skilled in the art.
Step iv)
In step iv) of the method according to the invention, the gaseous discharge
from the
evaporator is condensed and subjected to a separation, with recovery of the
dehydration product.
Suitable condensers are sufficiently known to those skilled in the art, for
example heat
exchangers such as, e.g., plate heat exchangers, spiral heat exchangers, tube-
bundle
heat exchangers, U-tube heat exchangers. The condenser is selected and
designed in
accordance with the requirements. The use of a total condenser is possible, as
also a
combination of a plurality of condensers connected in series. Preferably,
then, the
respective downstream condenser in the direction of flow of the gaseous
discharge is
operated at a lower temperature than the condenser situated further upstream.
A
fractional condensation of the gaseous discharge from the evaporator can
thereby be
achieved.
Preferably, the gaseous discharge from the evaporator is cooled in the
condenser to a
temperature in the range from -30 C to 70 C, preferably -20 C to 50 C.
Separation of the condensate can proceed by customary methods known to those
skilled in the art. Preferably, the condensate is subjected to a separation by
distillation.
Suitable devices for separation by distillation comprise distillation columns,
such as tray
columns, which can be equipped with bubble caps, sieve plates, sieve trays,
random
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packings, ordered packings, valves, side takeoffs, etc., evaporators, such as
thin-film
evaporators, falling-film evaporators, forced-circulation evaporators, Sambay
evaporators, and combinations thereof.
Preferably, the condensate is subjected to separation, with the following
streams being
obtained:
D1) a stream enriched in dehydrogenated carbohydrates, and
D2) a stream enriched in the solvent (LM).
Optionally, the discharge from the dealkylation zone can be subjected to a
separation,
with further streams being obtained. lf, e.g., in the method according to the
invention a
mixture is used as solvent, e.g. a mixture of water and at least one water-
miscible
organic solvent, the fractions D1) and/or D2) can comprise a plurality of
components
and each can be subjected to a further separation by distillation.
Alternatively, for the
separation by distillation, columns having side takeoffs, dividing-wall
columns, or
thermally coupled columns can be used which make possible separation of the
condensate into three or more fractions.
Generally, the fraction D1) comprises a main product in an amount of at least
50% by
weight, particularly preferably at least 75% by weight, in particular at least
90% by
weight. The main product present in the fraction is dependent, inter alia, on
the
hydrocarbon starting material used. Thus, e.g., when hexoses or a hydrocarbon
starting material which comprises predominantly hexose units are used, 5-
hydroxy-
methylfurfural is obtained as main product.
The resultant dehydration product can (according to desired purity and purpose
of use)
be used directly or after further work-up and/or purification. This includes,
e.g., use for
the synthesis of pharmaceuticals, polymers, macrocyclic compounds etc. 5-HMF
obtained by the method according to the invention can serve either directly or
after
derivatization as starting point for the synthesis of pharmaceuticals,
polymers and
macrocyclic compounds. Suitable 5-HMF derivatives are, e.g., 2,5-
furfuryldiamine, 2,5-
furfuryl diisocyanate and 5-hydroxymethylfurfurylidene esters, which can be
used for
producing polyesters, polyamides and polyurethanes.
The solvent (LM) recovered from the condensate or individual components
thereof can
be reused in step i) of the method according to the invention.
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The invention will be described in more detail with reference to the
following, non-
limiting, examples.
Examples
Figure 1 shows a device for carrying out the method according to the
invention. Two
controllable feeds, of which one serves for feeding a solution of the
carbohydrate in a
solvent (LM) and one serves for feeding an ionic liquid (IL) are combined and
fed into a
wiper-blade evaporator. The wiper-blade evaporator used is a Sambay
evaporator
made of HC steel having 0.1 m2 evaporator surface, four wiper blades and
Normag
motor. A top outlet is connected to cooler, condensate vessel and diaphragm
vacuum
pump. In addition, a bottom outlet with collecting vessel is provided.
Example 1
The evaporator is heated to 200 C internal wall temperature and the wiper-
blade speed
of rotation is set to 900 rpm. The evaporator is operated at a vacuum of 1
mbar. A feed
of 300 g/h of butylmethylimidazolium chloride (BMIM chloride) warmed to 80 C
and a
feed of 22.3 g/h of a mixture of fructose/methanol/water (1:1:1, g/g/g) are
metered
together and simultaneously into the Sambay evaporator. A gaseous discharge
of
421.1 g/h is taken off continuously, condensed in a cooler at -5 C and
collected in a
receiver vessel. The condensate is analyzed by HPLC. 2.02 g of 5-HMF/100 g
were
detected, corresponding to a yield of 8%, based on fructose.
Example 2
The procedure of Example 1 is followed, wherein, as ionic liquid,
methylimidazolium
chloride (HMIM chloride) is used. The evaporator is heated to 170 C internal
wall
temperature. A feed of 300 g/h of HMIM chloride heated to 80 C and a feed of
44 g/h of
a mixture of fructose/methanol/water (1:1:1, g/g/g) are metered together and
simultaneously into the Sambay evaporator. A yield of 10.1% of 5-HMF based on
fructose was detected.
